“It’s your DPF”, these are the all too frequent words spurted out to drivers of diesel cars from the car dealership.

What is a DPF?

We all remember when diesel cars used to pump out plumes of black smoke when started up or when accelerated hard, it really was very unsightly. The solution is a Diesel Particulate Filter, DPF, a unit fitted to the exhaust system in all new diesel engined cars to catch all this soot and burn it off safely.

How does it work?

The soot is captured in straw like compartments that are blocked so the build up of soot cannot escape under normal running conditions but once the DPF unit reaches a certain temperature it will ‘regenerate’ and the build up of soot will be pushed out clearing the DPF.

How do I regenerate my DPF?

There are two two types of regeneration, passive regeneration is when the DPF reaches a certain temperature naturally, this usually occurs at motorway speeds or when the car is accelerated very hard. And active regeneration which occurs when the car realises that the DPF is filling up and the car increases the temperature of the DPF and it is cleared.

That sounds good. Problem?

Yes, there are lots of problems, the DPF has to reach a certain temperature and many cars even at motorway speeds do not reach the required temperature, also the active regeneration does not clear the unit completely and they are becoming blocked on a regular basis.

Why are these things fitted?

Car manufactures are under pressure to lower the emissions and make cars greener, pressure from governments and customers alike, the DPF lowers the emissions considerably and once the build up of soot is burnt off nothing but ash is left. It should be a perfect solution – when they work properly.

What are the Manufactures doing?

It seems that garages are full of cars having their DPF fixed with a forced regeneration or an expensive replacement, they are all aware that its a problem but there is little they can do other than warn their customers at the point of sale. This is what Nissan put as a disclaimer in their brochure:

The 1.5 dCi, 1.6 dCi & 2.0 dCi engines fitted to QASHQAI+2 include a diesel particulate filter (DPF) to reduce emissions and help protect the environment. The functionality of a DPF may not be suitable for all customers. If your journeys are predominantly urban or low speed, a model without a DPF may be a more suitable alternative.

Should I panic?

No, not at the moment at least, your mobility car is fully covered and we have no records of customers having to dig into their own pockets to fix this problem – yet. The advice given is that you should not have a car with a DPF fitted if you only travel short distances, this is now becoming published advice from the manufactures – thus relinquishing them from any blame.

3 Comments

Eric Wignall

Posted April 27, 2013 at 6:26 PM

I have a Hyundai i40, 11 months old with 11,500 miles. The DPF goes into regeneration at least once a week and stays that way for a bout 3 days. The fuel consumption increases from 55-60mpg to 45-50mpg. In addition, the engine runs rough below 2000 revs when in regeneration. The Auto-Stop deactivate while in this state, but the warning light does not flash for 5 seconds as mentioned in the handbook, which is supposed to indicate a blockage. This has only been happening since I took it to the main agent for it’s first service. I have noticed that the engine was over filled with oil, but don’t know whether this has caused the problem.

Angela Paddock

Posted September 18, 2012 at 3:59 PM

I have a Hyundai IX35 and this DPF is causing me real problems and is becomming more frequent. I have spoken to JT Hughes but I never get a response